Holographic optical element based digital holographic interferometer for the study of macro flames, micro flames and their temperature instability

Abstract

Abstract In this communication, the measurement of flame temperature and flame temperature instability in macro, micro-sized flames using digital holographic interferometer based on volume phase holographic optical element is experimentally demonstrated. Volume phase holographic optical element (grating) recorded on dichromatic gelatine is used as a beam splitter to design digital holographic interferometer. Volume phase holographic grating will split the incoming light beam into zero, +1, −1 orders. The two beams (zero order and +1 order) can be made of equal intensities by slightly tilting the grating in the path of the beam. Volume phase holographic grating can be designed and fabricated to have high diffraction efficiency (≈90%) and remove stray light from the system reaching to the grating and will lower the coherent noise (speckle pattern). This will improve the contrast of interference fringes while recording the hologram and thus will provide better quality interferograms of temperature field. This type of system is expected to give more accurate measurements as noise due to the speckle pattern, and scattering will become almost negligible.